Develop native iOS apps in Go, on any platform, without the SDK!

[Splizard]

After successfully achieving exactly this with Android last week, there was still another major mobile platform to conquer, iOS!

Thankfully the community funding received so far ($289.69NZD) was just enough to cover the impulsive decision of mine to acquire a refurbished iPhone 8, I picked this version up as it's the lowest iPhone version supported by both Go + Godot and I got to work in the evenings to ensure that iOS development with graphics.gd could be just as accessible and well, the good news is, this was a lot easier than I expected!

So without further ado, I'm excited to share the IOS development workflow for graphics.gd :

1. Install SideStore onto an iOS device in the same local network as your machine.
2. GOOS=ios gd run.
3. Scan the QR code with that device and tap the SideStore prompt to install.
4. Launch the app from the iOS home screen.

Here's real-time footage of a cached re-compile of the graphics.gd Go shader sample project to iOS:
(It does take a moment to install, skip ahead or check out the important details below)

20250912_214904.webm

Now, I'll admit this isn't quite as quick or automatic as Android yet but my experience has shown that it's more than manageable and since you don't need a cable once it's setup, perhaps it's even better in a way!

Important Details

• No Apple Software nor Apple SDKs are bundled with, or downloaded by, graphics.gd.
• Projects can be built into an .ipa on any development platform (ie. Windows/MacOS/Linux).
• Everything is compiled into a single native binary.
• The only Apple account required for this process is the one on the iOS device.
• Free apple accounts without the Apple Developer License have restrictions of the number of different apps that can be installed this way (in practice, only a couple of them).
• The iOS device itself signs the app and (as I understand it) this meets Apple's requirements of restricting all of Apple's Software (including their Provisioning Profiles) to be used solely on Apple hardware.
• As such, apps built this way are unsigned, so without Xcode, they can only be installed via sideloading solutions such as SideStore or AltStore.
• It's possible to leverage the full iOS-supported capabilities of Go and Godot here, 2D, 3D, networking & more.
• Projects built with graphics.gd include an .xcodeproj that can be imported into Xcode as needed.

Behind the Scenes

For some time, I've been learning how Zig achieves libc cross-compilation for MacOS, which is very similar to iOS. Zig bundles an Open Source copy of the .tbd file used to dynamically link to LibSystem, it turns out these .tbd files are very simple .yml files that point at the library to link to and the list of symbols that can be located within that library. Here's what it looks like:

--- !tapi-tbd
tbd-version:  4
install-name: '/expected/path/to/dynamic/library/on/the/system' 
targets:
 - arm64-ios
 - arm64-macos
exports:
 - targets: [ arm64-ios, arm64-macos ]
   symbols:
    - do_something
    - another_func
   objc_classes:
    - SomeClass
...

So in order to cross compile almost anything to MacOS or IOS, all you need to do, is run the cross-compiler, represent the required headers (note, this is easier said then done) and then observe the inevitable undefined-symbols errors from the compiler and to figure out which symbols belong to which system library (often they have a prefix that helps you to figure this out).

Go already compiles to MacOS/iOS with very little C headers and since Godot already distributes static binaries for iOS, I could almost entirely skip the headers and instead simply had to add each undefined-symbol to the appropriate .tbd file. So piece-by-piece I did this for all of the symbols that Godot + Go needs on MacOS/iOS, and I'm bundling the result fully Open Source with graphics.gd.

As a consequence of this, graphics.gd enables natively-compiled iOS applications to be developed in Go on any platform!

[curioussavage]

Hello! First of all this super cool. I've been having a lot of fun writing a little game for my kids with it. But I really don't like the idea of having to side load the app onto their iPads.

Seems fine for dev and testing but is it actually possible at all to publish it on the iOS App Store?

[Splizard]

@curioussavage do you have a Mac OS device and/or an Apple Developer account?

If you do, then you can sign the .ipa with an App Store certificate and use Apple's "Transporter App" on the Mac to upload it to App Store Connect.

My understanding of the Apple TOS, is that the use of provisioning profiles requires apple hardware, so you would be looking for a way to sign the .ipa on the iOS device itself and then upload to App Store Connect from there, I don't think there are any barriers to doing this (SideStore already signs .ipas this way) but I'm not aware of any iOS apps that already support this use-case.

[curioussavage]

I do have MacOS and iOS devices. Can't remember if I have a developer account but I could set one up if not.

What I'm limited on is experience and time. If you are willing to try to go through the process and document it I could fund the effort

...after writing this I realize I might have misunderstood your comment about apps built this way not being able to be published. Seems I might just have to sign it via the Xcode cli? Or build it in Xcode?

[Splizard]

Thanks @curioussavage, it's on my radar, I'll let you know when I have more documentation on this.

[Splizard]

Seems I might just have to sign it via the Xcode cli? Or build it in Xcode?

That's correct, are you still looking for guidance here? Please let me know, if so, I can make some time to explore this over the weekend. I generally avoid Xcode at all costs, as it's particularly unwieldly to work with but yes. It's a matter of building the xcode project that's in the releases directory or using codesign on a MacOS machine to sign the .ipa and then you can upload it to the store with Transporter App, my preference is the latter. As it's easier to reliably automate.

[curioussavage]

I'm a vim guy so I generally prefer to stay in the command line if I can. May need some guidance on it but for now I'm having trouble building for iOS. I may need to open a separate issue unless it's just my env.

I'm getting a bunch of errors about undefined symbols when building with GOOS=ios

stuff like:

awinn@adams-MacBook-Pro go-space-empires % GOOS=ios gd build
error: undefined symbol: _$s11Coordinator7SwiftUI29UIViewControllerRepresentablePTl
    note: referenced by go-space-empires.xcframework/ios-arm64/libgodot.a(app.ios.template_release.arm64.o):l_got.$s11Coordinator7SwiftUI29UIViewControllerRepresentablePTl
error: undefined symbol: _$s20UIViewControllerType7SwiftUI0aB13RepresentablePTl
    note: referenced by go-space-empires.xcframework/ios-arm64/libgodot.a(app.ios.template_release.arm64.o):l_got.$s20UIViewControllerType7SwiftUI0aB13RepresentablePTl
error: undefined symbol: _$s4Body7SwiftUI3AppPTl
    note: referenced by go-space-empires.xcframework/ios-arm64/libgodot.a(app.ios.template_release.arm64.o):l_got.$s4Body7SwiftUI3AppPTl
error: undefined symbol: _$s4Body7SwiftUI4ViewPTl
    note: referenced by go-space-empires.xcframework/ios-arm64/libgodot.a(app.ios.template_release.arm64.o):l_got.$s4Body7SwiftUI4ViewPTl

[Splizard]

thanks for raising this @curioussavage, this looks like some additional symbols in the recently-released Godot 4.6 IOS build that I've missed, will fix. Looks like there is some Swift library usage now in Godot.

[Splizard]

@curioussavage alright whew, that was a bit more difficult then I originally expected, seems like zig's MachO linker doesn't quite work for iOS 13+ (it doesn't support LC_DYLD_CHAINED_FIXUPS) so I had to change the toolchain to use the LLVM/clang linker directly (ld64.lld).

If you update the gd command, this should all be taken care of next time you do a GOOS=ios gd run or GOOS=ios gd build !

go install graphics.gd/cmd/gd@release

[curioussavage]

had to change some things in xcode but I was able to build it there an deploy on my phone! I should have written down what I changed but I can do it again later an documen that. I did notice that when building for ios the godot pack file is not updated so I have just been copying it in there for now